Traffic incidents and road conditions impact the safety of drivers, passengers, and vehicles. It is desired to disseminate such road related information to using a multi-hop wireless broadcast network to ensure the safety of the drivers, and passengers and vehicles. This can alleviate traffic congestion, speed up medical rescue and provide real-time data acquisition for law enforcement and insurance purposes.
In traffic incidents, often, multiple vehicles are involved. People may be injured, vehicles damaged, and insurance claims need to be processed. In such situations, evidence and witnesses are necessary to correctly identify fault.
Chen et al., in “Ad Hoc Relay Wireless Networks over moving vehicles on roads,” ACM MobiHoc 2001, describe opportunistic and pessimistic forwarding of information. Opportunistic forwarding buffers data messages, and then forwards the messages as soon as possible. Opportunistic forwarding can result in prolonged delays and is more suitable for delay-tolerant applications. Chen et al. do not consider the topology and environment in which the vehicles operate, the content of alert messages, multi-vehicle accidents, and the effectiveness of warning message propagation.
Niculescu et al., in “Trajectory-based Forwarding and its Applications,” ACM MobiCom 2003, route messages along a predefined curve. The method is a combination of source routing and Cartesian forwarding. A trajectory for messages is determined by a source node, and other nodes in the network forward messages based on their relationship to the trajectory. Their approach is designed for ad hoc networks, not vehicular networks.
Nekovee et al., in “Reliable & Efficient Information Dissemination in Intermittently Connected Vehicular Ad Hoc Networks,” IEEE VTC 2007, describe epidemic protocols for information dissemination. They assume that each vehicle has knowledge of its location using a global positioning system (GPS). Each message contains the location of the source node, i.e., the vehicle, and a direction of propagation. For omni-directional broadcast, a random delay before broadcasting the message is exponentially biased towards vehicles that are further away from the source node. That method improves the speed at which the information is disseminated through the network, but it does not control how much information needs to be disseminated as a function of distance away from the alert source.
Lochert et al., in “Probabilistic Aggregation for Data Dissemination in VANETs,” VANET Conference 2007, describe a method for probabilistic aggregation for data dissemination. Their aggregation technique is based on using Flajolet-Martin sketches. The aggregation technique reduces the amount of information required to transmit in the air. However, the accuracy of information is not assured. While their technique can be applied to non-crucial information such as parking space, it cannot be used for safety critical messages.
Eichler et al., in “Strategies for Context-Adaptive Message Dissemination in Vehicular Ad Hoc Networks,” IEEE V2VCOM, 2006, describe context-adaptive message dissemination. Each vehicle (node) only forwards a message if it obtains benefits by doing so. Each node considers if it is interest in the information before forwarding the message.
Little et al., in “An Information Propagation Scheme for VANETs,” IEEE ITS Conference, 2005, describe a cluster-based method. Clusters are formed continuously regardless of whether accidents have occurred or not. In addition, each cluster designates a cluster head. Data are propagated whenever there is contact of one cluster with another. Cluster headers and trailers are present in each cluster message. Their approach relies on clusters in opposite lane to relay messages. Details on cluster formation, size and membership are not described.